Structure and Biological Dynamics of the Oligotrophic Ocean Photic Zone off the Hawaiian Islands

Abstract

The base of the photic zone, as defined by the 1-percent light depth and discontinuance of photosynthetic carbon fixation, was determined to be at 130140 meters on stations off the Hawaiian Islands. Measurements, including radiant energy transmission, plant nutrients, and chlorophylls, were made in the depth interval 0-250 meters. The numerical vertical abundance, biomass, and the identity of phytoplankton, microzooplankton, bacteria, and fungi were determined. A discussion of the biological dynamics within this photic zone is based on these observations and on measurements of photosynthetic production, nitrogen fixation, and other microbial activities.